Hey dpt2b4me,
Just relax, the atmosphere is casual. Before the interview you'll be sitting with other candidates in the waiting room along with some LLU PT students. The PT students are there to answer any questions you have and to possibly help with the candidates who are nervous. Be ready to give detailed and awesome answers 1) why did you choose PT, 2) why did you choose LLU, and 3) the awkward broad question "So, tell me about yourself." You guys may already know this, but as far as attire--it's professional (suite & tie).
When I went in for my interview I was a nervous wreck, I could not sleep the night before and had no appetite. But once the interview began the way the questions were phrased by the interviewer it became causal. I was only asked why LLU, then I asked about 5 questions, then my interviewer and I started talking football; and that's what we were talking about the remainder of the time. I was told by my interviewer that I scored high. Unfortunately that wasn't good enough for me to get a seat due to GPA. So my scores are being used for this cycle, which is the same for other "2nd-timers."
Hope this help!